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1. What do we call this syndrome?

‘Feline asthma’ most widely used term; may be some differences however from asthma in peopleOther terms that have been used to describe inflammation of the lower airways in cats without an identifiable cause include feline bronchial disease, feline lower airway disease, and feline allergic airway disease.

2. Pathogenesis:

Complex and multifactorial but allergens or non-specific airway irritants likely to be involved in initiating or at least exacerbating airway inflammationRelationship between respiratory infection and feline bronchial disease remains to be clarifiedAllergens/irritants thought to trigger airway Type I hypersensitivity reaction which results in:

Bronchial inflammation

Mucosal oedema

Bronchoconstriction

Mucus gland hypertrophy and excessive mucus secretion

Airway hyper-reactivity

Net result is LOWER AIRWAY OBSTRUCTION.

Signs may be acute and episodic but reversible, while in others chronic inflammation results in irreversible fibrosis and emphysema.Eosinophils likely primarily involved in inflammatory response but eosinophilic airway inflammation not specific to asthma

Hallmark features:

Airway inflammation

Airway hyper-reactivity or hyperresponsiveness

Limitation of airflow

Potential airway remodelling

3. Who gets feline asthma?

Basically any catClinically most prevalent in young- to middle-age cats – some cats may have chronic subclinical pathology for some time before clinical episodeSiamese cats may be over-representedPrevalence of chronic subclinical asthma unknown

4. Clinical findings:

Spectrum with respect to both severity and frequencyChronic, intermittent cough through to acute, episodic respiratory distressAcute clinical signs most commonly include coughing, and variable degrees of tachypnoea or dyspnoea; latter can be very severe, potentially life-threatening.Lung auscultation may reveal harsh lung sounds potentially with wheezes on expiration and sometimes crackles.‘Expiratory push’ may be present but not always.Should not exclude asthma just because wheezing or expiratory push is absent

Airway rupture due to asthma will result in spontaneous pneumothorax – dull lung sounds dorsally or diffusely if severe.

Some reports of asthmatic cats presenting with episode of vomiting during an episode of paroxysmal coughing or hacking rather than respiratory distress.

5. Diagnosis:

Presumptive emergency diagnosis typically on basis of consistent clinical findings, exclusion of other differential diagnoses that could lead to an acute dyspnoeic episode, and especially positive response to appropriate therapy.

More definitive diagnosis only after adequate stabilisationNo one gold standard test. Diagnosis on the basis of supportive data collected from thoracic radiography, bronchoscopy and bronchoalveolar lavage (BAL) analysis, both cytology and culture. Exclude other causes of lower airway disease.

6. Thoracic radiography:

***Only at appropriate time. Think risk-benefit analysis at all times.***

Abnormalities may include a bronchial, interstitial, alveolar or mixed lung patternSevere diffuse bronchointerstitial lung pattern may be identified with some frequencySevere lower airway obstruction may result in air trapping and lung hyperinflation; identified radiographically as increased pulmonary radiolucency and flattened caudally-displaced diaphragm.

Parenteral glucocorticoids mainstay of acute life-saving therapyAdjunctive parenteral bronchodilator – DO NOT use as sole therapy in an acute case:

β2-adrenergic receptor agonist, e.g. terbutaline

Methylxanthines, e.g. aminophylline

8. Treatment – Subacute and Chronic:

Time to inclusion of additional topic therapies and transitioning to oral therapies depends on individual cat’s progress and level of tolerance for topical/oral therapiesOral prednisolone: dose and the duration of therapy depends on individual cat’s response and whether topical therapy is also being usedIf inhaled glucocorticoids are also being used and the patient is doing well with good compliance, prednisolone can be tapered and discontinued more quickly.

Topical glucocorticoids (e.g. fluticasone):Should not be used alone in an acute crisis; may be used additionally if patient is tolerant.Going forward they offer an attractive alternative with a significantly lower risk of side-effects compared with systemic glucocorticoidsBut can be expensive and not all cats are tolerant; patient compliance can be improved by gradual introduction with period of sensitisation to topical administration.

Fluticasone:Administered by metered dose inhaler attached to spacer device and face mask (e.g. AeroKat® Feline Aerosol Chamber)Thought to have low systemic bioavailability following inhalation so generally not associated with adverse effects seen with long-term prednisolone useUnclear but may take up to 2 weeks to reach maximum efficacy

Topical bronchodilator – e.g. inhaled albuterol:Short-acting β2-agonistSome data suggesting should not be used on daily basis; may be better kept as a potential rescue therapy

9. Alternative or novel therapies?

Some combination of glucocorticoids and bronchodilators is usually effective in managing most asthmatic cats and glucocorticoids at any rate are pretty cheap.Why might alternative or novel therapies be attractive? Reasons include:

Cats that cannot be well controlled with the standard approach

Cats in which chronic glucocorticoids have unacceptable adverse effects

Cats in which glucocorticoids are absolutely or at least relatively contraindicated from early on (e.g. diabetic)

And… current therapies may control the syndrome adequately but they may not necessarily be directly addressing the cause of the problem, i.e. hypersensitivity immune system dysfunction.Directly tackling immune dysfunction may prevent chronic structural lung changes (remodelling, irreversible fibrosis) and potential long-term lung dysfunction.

Allergen-specific immunotherapy:Carers of asthmatic cats should be questioned at length and advised extensively about possible allergens (e.g. cat litter, cigarette smoke, carpet cleaners, air fresheners) in the home and importance of minimising the cat’s exposure to them.BUT If specific inciting allergens can be identified by testing then allergen specific-immunotherapy may be possible and may become increasingly available in the clinical setting.

10. Cyclosporine:

Recent case report (Nafe, Leach, 2014 – see below) in which this was used to treat a cat with asthma.

Abstract: “A 5-year-old domestic shorthair cat that had been previously diagnosed with diabetes mellitus was presented for episodes of coughing and respiratory distress. Diagnostic testing revealed congestive heart failure secondary to hypertrophic cardiomyopathy and concurrent asthma. All clinical signs and eosinophilic airway inflammation resolved with oral ciclosporin while concurrently receiving medications for treatment of heart failure (furosemide and enalapril). Ciclosporin should be considered for treatment of feline asthma in patients with concurrent diseases (eg, diabetes mellitus, severe heart disease) that may contraindicate use of oral glucocorticoid therapy.”

At the time the cyclosporine was used in this cat patient would be classified as chronic with variable clinical signs; NOT used as part of stabilising an acute crisisTreated with cyclosporine for 3 weeksEvidence for beneficial effect:Improvement in cough and tachypnoea at homeImprovement in inflammatory cytology from consecutive blind BAL samples

Cyclosporine was tapered off while inhaled fluticasone was introduced; then maintainedon this. Done to minimse costs and potential adverse effects of long-term cyclosporine use.

Cyclosporine relatively well known as an immunomodulatory agent. Typically used as adjunctive or second-line agent in immune-mediated disorders; also e.g. in allergic dermatitis. Can be considered as sole agent in glucocorticoid-intolerant cases.Appears to be relatively well tolerated in cats

Having said that the evidence base for cyclosporine use in cats in general is still relatively scant and much more is needed. With respect to use in asthma, need to bear in mind this is just a single case report of a cat with a specific set of circumstances.

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